At present, when a mobile telephone is used in vehicle, the transmitting power of the mobile phone in vehicle is required to be smaller than a certain standard value. European patent No. EP 0,692,885 A1, titled “Wireless Telephone”, disclosed a wireless telephone apparatus comprising a portable wireless telephone set, an adapter and a car-kit, wherein the adapter includes a section of hand-free circuit coupled with the controlling section of the portable wireless telephone set through a controlling signal line; the wireless telephone set is coupled with the adapter through the coupling of the high-frequency signal, so that the signal of the wireless telephone is sent to an amplifying means of the car-kit through the adapter, amplified there and transmitted to the air from the antenna of the car-kit rather than the antenna of the telephone itself. Thus, when a mobile telephone or a portable telephone is used in vehicle, the telephone set will not have to be held in hand, and the speech information will enter directly the mobile phone or the portable phone through the section of hand-free circuit of the adapter; however, the transmitting power of the mobile phone in vehicle has to be higher, not conforming to the European standard in the future.
Alternative U.S. Pat. No. 5,524,044 disclosed that the mobile terminal will decrease its own transmitting power to a predetermined value when it has detected itself being coupled with the adapter of the car-kit so as to maintain the smaller transmitting power in vehicle, and after the mobile terminal is coupled with the adapter, it will switch off the connection of the RF module and the antenna of the mobile terminal using a changeover switch, so that the RF signal of the mobile terminal will be transmitted by the antenna of the adapter instead of its own antenna. However, in this patent documents, the changeover switch must be provided in the mobile terminal, and it is by the signal line that the mobile terminal is coupled with the adapter.